A valve arrangement of the kind mentioned above and a method for operating a valve as mentioned above are known from GB 2 452 043 A. The first temperature sensor detects the ambient temperature of a room. The second temperature sensor detects a temperature in the vicinity of the valve. The temperature detected by the second temperature sensor is used to calculate a compensation value for the first temperature sensor so that the ambient temperature can be determined with a greater accuracy.
EP 1 235 130 A2 describes a method and an apparatus for controlling a room temperature using two temperature sensors, one of which senses the room temperature and the other of which senses a temperature near the valve. Both temperatures are combined to get more reliable information about the actual room temperature.
A thermostatically controlled valve compares the actual room temperature with a set room temperature and increases the flow of heating fluid, when the actual room temperature is below the set room temperature, and decreases the flow of heating fluid, when the actual room temperature is higher than the set room temperature. In most cases this leads to a slightly oscillating movement of a valve element relative to a valve seat. Such a movement needs energy. When the actuator is driven electrically, waste of energy should be avoided.
Furthermore, for a sophisticated control of the valve, information is necessary about the opening degree of the valve, e.g. the position of the valve element relative to the valve seat.
When an electrically driven actuator is used, this information can be obtained by driving the valve in closing direction until the force necessary to move the valve element increases dramatically. This increase is an indication that the valve element has touched the valve seat and sealing means are compressed. However, such detection requires a large amount of electrical energy as well since the current consumption is non-linearly increasing with the force applied.